Let $y=y_{1}(x)$ and $y=y_{2}(x)$ be two distinct solutions of the differential equation $\frac{d y}{d x}=x+y$, with $y_{1}(0)=0$ and $y_{2}(0)=1$ respectively. Then, the number of points of intersection of $y=y_{1}(x)$ and $y=y_{2}(x)$ is
Solution
<p>${{dy} \over {dx}} = x + y$</p>
<p>Let $x + y = t$</p>
<p>$1 + {{dy} \over {dx}} = {{dt} \over {dx}}$</p>
<p>${{dt} \over {dx}} - 1 = t \Rightarrow \int {{{dt} \over {t + 1}} = \int {dx} }$</p>
<p>$\ln |t + 1| = x + C'$</p>
<p>$|t + 1| = C{e^x}$</p>
<p>$|x + y + 1| = C{e^x}$</p>
<p>For ${y_1}(x),\,{y_1}(0) = 0 \Rightarrow C = 1$</p>
<p>For ${y_2}(x),\,{y_2}(0) = 1 \Rightarrow C = 2$</p>
<p>${y_1}(x)$ is given by $|x + y + 1| = {e^x}$</p>
<p>${y_2}(x)$ is given by $|x + y + 1| = 2{e^x}$</p>
<p>At point of intersection</p>
<p>${e^x} = 2{e^x}$</p>
<p>No solution</p>
<p>So, there is no point of intersection of ${y_1}(x)$ and ${y_2}(x)$.</p>
About this question
Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree
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